This invention relates to a process for producing a 3-pentenoic ester through hydroesterification reaction of butadiene on an industrial scale, and particularly relates to a process for producing a 3-pentenoic ester which comprises hydroesterification of butadiene in the presence of cobalt carbonyl catalyst, characterized by using a reaction medium composed of at least two solvents selected from compounds having pyridine ring, compounds having quinoline ring and compounds having isoquinoline ring.
Many processes for producing 3-pentenoic esters in which butadiene, an alcohol and carbon monoxide are reacted are known to those skilled in the art. For example, a process for producing a 3-pentenoic ester which comprises reacting butadiene, an alcohol and carbon monoxide in the presence of dicobalt octacarbonyl as a catalyst and a tertiary amine as a solvent and a process for producing a 3-pentenoic ester which comprises reacting butadiene, an alcohol and carbon monoxide in the presence of cobalt carbonyl complex synthesized from cobalt carbonyl and a tertiary amine are known from Bulletin of the Chemical Society of Japan vol. 46 (1973) 524-530 pages. However, according to the above processes 3-pentenoic esters as well as by-products, such as 4-vinyl-1-cyclohexene, dibutyl ketone, methylglutarate and high boiling materials derived from polymerization of butadiene are formed. Therefore, selectivity to a 3-pentenoic ester becomes low. Japanese Patent Publication No. 10935/1974 discloses a process for producing a 3-pentenoic ester which comprises hydroesterificating butadiene in the presence of cobalt carbonyl as a catalyst and pyridine as a solvent. However, a large amount of expensive cobalt carbonyl has to be used in order to increase yield of the 3-pentenoic ester according to this process; that is, cobalt carbonyl is required in order to selectively control hydroesterification reaction of butadiene and prevent forming of high boiling materials derived from polymerization of butadiene and other by-products.
In the working examples of Patent Publication No. 10935/1974, the amount of cobalt carbonyl catalyst used is 0.04 moles per 1 mole of butadiene. However, we found that when either one of pyridine or isoquinoline is used as a solvent, more than 0.1 mole of dicobalt carbonyl compound is necessary per 1 mole of butadiene. Even when a large amount of cobalt carbonyl catalyst is used, the invention of Patent Publication No. 10935/1974 results in forming by-products, such as 4-vinyl-1-cyclohexene, dibutyl ketone, methyl glutarate, high boiling materials derived from polymerization of butadiene and the like. Therefore, the yield of 3-pentenoic ester and selectivity to 3-pentenoic ester according to the process of Patent Publication No. 10935/1974 are not necessarily satisfactory. One of the most important factors in practicing the process industrially is how to recover the expensive catalyst effectively. The prior methods for recovering the catalyst are costly. So, at present in case of producing a 3-pentenoic ester from butadiene the main point of interest is how to reduce the amount of catalyst employed.